Oleaginous seed materials, such as soybeans, cottonseeds peanuts, sesame seeds, sunflower seeds, rapeseed, and the like contain proteinaceous matter of a highly nutritious nature. Soybeans for example, after oil extraction, have been treated to recover the proteinaceous matter for use in diverse industrial processes, e.g. in the papers, plastic and food industries. Without limitations as to other uses, the invention will be herein particularly described in connection with the extraction of oil from soybeans.
In the processing of seeds to extract oil by solvent extraction, the seeds are crushed or milled into cake or flakes or otherwise fragmentized and treated with a solvent to extract the oil, leaving meal in which vaporizable solvent remains. By heating the meal, using steam both indirectly through a heated surface and/or directly by steam contacting the meal, the solvent is vaporized while the meal itself is cooked or toasted to carmelize carbohydrates, to deactivate certain enzymes and to denature proteins thereby to produce an edible substance.
Apparatus for vaporizing the solvent so that it might be recovered while simultaneously and/or subsequentially toasting the extracted seed is well known in the art as illustrated, for example, in the U.S. Pat. Nos. 1,112,128; 2,577,010; 2,585,793; 2,695,459; 2,806,297; 3,018,564; and 3,359,644. As disclosed in these patents, the material from which solvent is to be removed progresses downwardly as a bed through a column which is provided with spaced horizontal plates therein dividing the interior of the column into a vertical series of compartments. In these compartments, the material is heated and agitated and the finished material discharged from the bottom of the column.
A solvent is removed as an overhead vapor from the column which is then condensed. Present desolventizing practice include the introduction of steam directly into the desolventizer toaster tower or column from a boiler via suitable piping including valves, orifices, etc., to reduce the pressure of the steam to that necessary for sparging the bed to accomplish desolventizing operations, i.e. steam flows into the flakes on the trays through holes provided in the sparge tray, the sparge arms or like devices. The sparger steam condenses on the flakes while vaporizing the bulk of the hexane and providing the sensible heat to raise the temperature of the flakes to about 190.degree. to 205.degree. F. Such temperatures are adequate to denature the proteins and deactivate the enzymes provided adequate residence times are attained during passage of the meal through the desolventizer-toaster tower and drying apparatus.
Generally, the moisture content of soymeal exiting the desolventizer-toaster tower is from 17 to 25 percent by weight dependent on the temperature of the discharged meal. Since commercially saleable animal soymeal feed should contain not more than about 12 percent by weight moisture, external drying is generally effected on the desolventized-toasted soy meal in commercially available rotary drum type apparatus having large indirect heat transfer surface per unit volume. Traces of solvent vapor are discharged from the dryer into the atmosphere and are considered a pollutant subject to environmental consideration via the Clean Art Act. Additionally, the desolventizer-toaster operation is usually performed in expressive equipment requiring, inter alia, considerable energy, steam and electrical power. Additionally, there are requirements for considerable amounts of make-up to the recycle solvent stream, etc.